The term “retarder” is understood herein to be an electrical eddy-current brake, which is intended to reinforce or replace the service brake, for instance of rail vehicles, utility vehicles, or the like in certain situations. The braking action of a retarder arises from the buildup of a magnetic field, which counteracts the rotation of a rotor because of the induction of eddy currents in the rotor. The rotor is connected, for instance to the cardan shaft of the vehicle, in a manner fixed against relative rotation. The magnetic field can be generated for instance by four magnet coils or pairs of magnet coils, which can each be added in succession depending on the braking power individually required. One such retarder is described in detail in German Patent Disclosure DE 39 08 234 A1, for instance, which is hereby expressly incorporated by reference in its full content in the disclosure of the present application.
From Japanese Patent Disclosure JP 61266064, a rotor with the characteristics recited at the outset is already known. According to this, it is provided that an eddy current brake be used in a rail vehicle; the rotor is connected to the wheel axle in a manner fixed against relative rotation, and the stator comprises coils disposed on both sides of the rotor. A disadvantage of the known apparatus is the low braking action, which can be ascribed to the fact, among others, that the coils are distributed over only approximately a semicircle of the rotor.